This invention relates to a disposable electrosurgical blade or active electrode used to perform electrosurgical procedures and to a method manufacturing such a blade. More particularly, the present invention relates to a new and improved electrosurgical blade exhibiting release characteristics as a result of having a relatively thin and uniform cross-sectional coating of nonstick material comprising silicone which is directly adhered to and supported on a metallic body of the blade. Even more particularly, the present invention relates to a new and improved method of fabricating an electrosurgical blade having non-stick, release characteristics by steps involving adhering a nonstick coating comprising silicone to an oxide of the metal body, thereby avoiding the typical requirements for mechanically roughening the metal body to achieve adequate adhesion or for applying intermediate layers of primer materials or multiple layers of materials to attain the desired characteristics.
In general, electrosurgery involves the application of relatively high frequency or radio frequency (RF) current to living tissue. Depending upon the characteristics of the RF signal, electrosurgery is used to cut tissue, to coagulate bleeding (hemostasis) from the tissue or to both cut and coagulate simultaneously. The typical frequency of the electrosurgical current is from approximately 400 kHz to 750 kHz, because this frequency range avoids stimulating the nervous system. The electrical power applied can vary from a few watts for delicate neurosurgical procedures to approximately 300 watts for cutting substantial tissues in open surgical procedures. The open circuit voltage prior to energy transfer into the tissue may be in the range of 5,000-10,000 volts peak to peak. Of course, the voltage drops substantially as the current flow increases through the impedance of the tissue. Typical tissue impedances range between about 10 ohms and 500 ohms.
Electrosurgery is performed by connecting the electrosurgical blade or active electrode to an electrosurgical generator, activating the generator to supply the electrosurgical waveform, and delivering the energy of the electrosurgical waveform to the tissue through the blade. The blade is positioned in a pencil-like handpiece which the surgeon manipulates to achieve the desired effect at the surgical site. Selecting and adjusting the characteristics of the electrosurgical waveform delivered by the electrosurgical generator allows the surgeon to cut the tissue, to coagulate bleeding from the tissue, or to simultaneously cut and coagulate. The ability to control the application of electrical energy to the tissue to cut and coagulate tissue is one of the substantial advantages of electrosurgery, and such advantages contribute to the use of electrosurgery in most major surgical procedures.
The physical characteristics of the typical electrosurgical blade also are used advantageously by the surgeon to accomplish different surgical procedures. The typical electrosurgical blade has an elongated working area with a shape similar to a rectangle in cross-section. Two relatively-broad and generally-parallel sides extend along and exist on opposite sides of the working area. The two broad sides are joined by a narrow edge which extends between the broad sides and which curves around a distal end or tip of the working area. The edges form the narrow legs of the cross-sectional rectangle while the broad sides form the wide legs of the cross-sectional rectangle.
Cutting is achieved by bringing the narrow edge into close adjacency with the tissue. A high current density at the narrow leading edge transfers energy into the tissue as relatively short arcs, thereby causing enough heat to explode or rupture the cells of the tissue at the interface with the narrow leading edge. The tissue separates at the leading edge leaving a well-defined incision. It is in this manner that the current from the electrosurgical blade cuts the tissue, rather than the tissue being separated from the physical contact and mechanical action of a sharp edge, as is the case with a traditional scalpel. Indeed, the narrow edge of the typical electrosurgical blade is not sharp and cannot cut tissue as a result of mechanical action. The separated tissue passes by the broad sides of the working area of the active electrode as the surgeon guides the blade, while the electrical energy creates the incision.
Coagulating bleeding surfaces usually involves bringing the tip of the working area of the blade to a point spaced slightly above the bleeding surface and delivering a duty cycle type of coagulating electrosurgical waveform. The duty cycle coagulating waveform includes an on time period during which the high frequency electrical signal is delivered, followed by an off-time during which no electrical energy is delivered. The coagulating duty cycles are repeated at a frequency in the neighborhood of approximately 30 kHz, with a power of approximately 50-80 watts. Longer arcs of electrical energy are transferred in a spray-like manner from the tip of the blade and these arcs penetrate into the tissue to create a reticulum which both activates the normal clotting mechanism in the blood and thermally seals the surface of the tissue. Bleeding vessels are coagulated in much the same manner except that the tip of the blade is sometimes placed in close adjacency with the severed vessel, causing the arcs to be concentrated at that location.
Simultaneous cutting and coagulating occurs by blending the duty cycle coagulation waveform with a continuous waveform. In general, this involves increasing the on-time of the duty cycle to sufficient amount which permits cutting to occur but which still allows coagulation to be achieved. Because of the relative convenience and quickness with which coagulation can be achieved, many surgical procedures will usually progress more rapidly by using electrosurgery than if electrosurgery was not used.
The bursting cells release cell protein and fluids into contact with the surface of the electrosurgical blade. Blood also contacts the surface of the electrosurgical blade as the tissue is severed and when the surgeon uses the electrosurgical blade to coagulate blood flow. Different types of tissues emit other types of body fluids into the surgical field, and these other body fluids may contact the electrosurgical blade.
The amount of electrical energy delivered to the tissue through the electrosurgical blade is sufficiently high so that the current flow through the blade itself heats the blade. Since the typical tissue impedance ranges in the neighborhood of tens of ohms to a few hundreds of ohms, the impedance of the blade itself is significant enough relative to the impedance of the tissue that the blade absorbs enough of the transferred energy to increase its temperature significantly during electrosurgery. The increased temperature of the blade causes the cell fluids, body fluids and blood to dehydrate, denature and accumulate on the blade in the form of a crust-like buildup. Unless periodically removed, the crust-like buildup increases as the blade is used.
The crust-like buildup is a significant distraction to the surgeon. The crust-like material negatively affects the electrosurgical performance. The crust-like buildup spaces the blade from the tissue, thereby making it difficult or impossible to transfer energy into the tissue to achieve the desired electrosurgical effect. The crust-like buildup on the broad sides of the blade also causes the blade to drag against the tissue at the incision, thereby creating an undesirable xe2x80x9cfeelxe2x80x9d when manipulating the instrument. The crust-like buildup may obscure the vision of the surgeon at the expected location of energy delivery from the blade into the tissue, thereby making it more difficult to achieve the precise effect desired. The problem and consequences of the crust-like buildup on electrosurgical blades has been recognized as a significant issue in electrosurgery for many years.
One approach to removing the crust-like buildup has been for the surgeon to periodically scrape the blade as clean is possible, perhaps by using scalpel or other tool to scratch the strongly-adhering, crust-like material off of the broad sides of the blade. Generally speaking, because most of the energy transfer is through the narrow edges during cutting and coagulation, this energy transfer tends to keep the narrow edges clean. Consequently, the buildup of crust-like material on the broad sides of the blade is the most significant distraction. Another approach to removing the buildup has been to use specifically-designed mechanical cleaning devices into which the surgeon could insert and withdraw the blade to scrape or otherwise clean off the buildup. The mechanical scraping and cleaning techniques are generally not preferred by surgeons because the scraping activity itself prolongs the surgical procedure. Moreover, scraping is generally not fully effective in removing all of the crust like material, but is better than no attempt to remove the buildup from the blade whatsoever. Consequently, the necessity to scrape the blade during the surgical procedure has been tolerated by surgeons.
Another approach to avoiding the crust-like buildup on electrosurgical blades has been to coat the exterior of the blades with a nonstick or release coating. The nonstick or release coating minimizes the adherence of the crust-like materials. The release coating allows the buildup to be removed more conveniently by a wiping action rather than a scraping action. The nonstick, release coating is primarily effective on the broad sides of the blade because the intense energy transfer from the narrow edges usually eliminates any coating on those surfaces after the blade is used. Since the broad sides of the blade are the primary location where the buildup normally occurs, the existence of the nonstick release coating on the broad sides achieves the primary benefit.
A variety of different types of release coating materials have been applied to electrosurgical blades, all with varying degrees of success and preference by surgeons. Among the types of release materials which have been used on electrosurgical blades are fluorinated hydrocarbon materials (similar to xe2x80x9cTeflonxe2x80x9d), silicone (polysiloxane), ceramic composites, and paralyene polymers, among others. These substances have been used on electrosurgical blades primarily because of their nonstick or release surface characteristics. Other factors which influence the choice of such materials for coating electrosurgical blades involve biocompatibility, heat resistance, dielectric strength, and adherence, among others.
Adherence is a particularly important characteristic, because the nonstick, release material should remain on the broad sides of the blade, despite the relatively high temperature of the metal blade and the occasional electrical arcing from the broad sides to the adjoining tissue. Because of the desire for good adherence, the typical approach has been to mechanically roughen the metal body prior to applying the release or nonstick coating. Mechanically roughening the surface of the metal body increases the surface area of the metal body by creating a large number of mechanical peak and valley aberrations into an otherwise smooth surface. The increased surface area and the texture of the peaks and valleys provides a complex mechanical structure to which the coating material will adhere with increased tenacity. Typical mechanical roughening techniques involve grit blasting, etching, burnishing, or knurling. Another roughening technique is to fuse a layer of textured material to the smooth surface. The fused textured material causes the release coating to adhere.
While the roughened surface achieves the objective of enhanced adherence of the release material, it also creates certain undesirable characteristics. Each of the peaks of the roughened surface presents a minuscule elevated point source from which an electrical field gradient exists when the metal body of the electrosurgical blade is energized with high voltage. Field gradients are responsible for initiating arcs of the electrical energy. In most circumstances, the arcs should not be initiated from the broad sides of the electrosurgical blade, but instead should be encouraged to form mostly from the narrow edge or tip of the blade. The corners where the broad sides join the narrow edges create the desirable field gradient locations for the initiation of the arcs to deliver the energy for cutting and coagulating as described above. Arcing from the points of the roughened broad sides of the blade may have the tendency to destroy the nonstick or release coating material on the broad sides by erupting the coating from the points were the arcs initiate from the peaks. Of course, destroying the nonstick coating on these broad sides diminishes or destroys the nonstick and release characteristics of the blade.
One technique of avoiding the undesirable point-source field-gradient effects of the roughened surface is to apply thick or multiple coats of release or nonstick material to the blade. Once the coating has been built up to a sufficient thickness, enough electrical insulation exists to eliminate or inhibit the arcing from the broad sides. However, applying multiple coats of material to the blade increases its manufacturing cost. The width of the blade between the coatings on the broad sides is also increased by the added width of the multiple layers of coatings. The increased width creates more drag on the adjoining tissue as the blade cuts.
Some types of nonstick or release coatings, particularly those consisting primarily of silicone (polysiloxane), have the tendency to develop hair-like fingers which extend out from the outer surface of the coating. This effect is referred to as xe2x80x9cblooming,xe2x80x9d and appears to result from the type of silicone used and/or the techniques used to cure it, such as gamma ray or other high-energy curing techniques. The hair-like fingers may continue to grow or develop with time, after the time when the silicone coating is otherwise considered to be initially cured. Such fingers cause additional surface area and present the opportunity for the crust-like material to adhere to the coating, even though the coating material itself is a release type of coating. It may be possible that the hair-like fingers break off from the remaining coating during use of the blade.
The recognized technique of achieving adequate adherence of the release or nonstick coating is to mechanically roughen the surface of the metal blade body. Typically the metal blade body is formed of stainless-steel. After roughening the stainless-steel body, it is also typical that a primer coat the applied before the release coating is applied to the primer coat. The primer coating adheres to the roughened metal of the blade body, and the primer coating also provides a surface to which the release or nonstick coating adheres. Some types of release coating materials contain a self-priming component, such as an adhesive resin, but even using these types of materials have required roughening of the surface before their application. While this surface-roughening technique achieves adequate adherence of the release or nonstick coating, it increases the cost of manufacturing the electrosurgical blade because of the added requirements for roughening the surface and applying multiple coatings of different types of materials.
The applicants are aware of one instance where a fluorinated hydrocarbon release coating has been directly applied to the stainless-steel metal body of an electrosurgical blade without first mechanically roughening the surface. In this situation, the stainless-steel blade was thermally oxidized for the purpose of cleaning the blade body by burning off or driving off foreign substances. The fluorinated hydrocarbon material contained an inherent primer or binder which caused the fluorinated hydrocarbon coating material to adhere. The fluorinated hydrocarbon material was sprayed onto the blade, and typically resulted in a thickness of between 0.0007 to 0.0015 inches.
It is with respect to these and other background considerations that the present invention has evolved.
One aspect of the present invention relates to a stainless steel electrosurgical blade which has a single, relatively thin and uniform layer of a silicone release material applied directly onto the stainless steel blade portion without applying one or more coatings of primer materials, without applying multiple layers of the release material, or without mechanically roughening the metallic body of the active electrode. Another aspect of the invention involves achieving adequate adherence of silicone nonstick or release materials to a stainless steel body of an electrosurgical blade without the necessity of mechanically roughening the blade body. A further aspect of the invention relates to eliminating the peaks and valleys caused by mechanically roughening the sides of an electrosurgical blade, and by so doing, substantially reducing or eliminating the prospects of unintended arcing through the release coating from point source field gradients at the peaks of the roughened surface. A further aspect of the invention involves a discovery that an oxide formed from iron of a stainless steel metallic body of the active electrode is sufficient to adhere a nonstick, release material comprising substantially polysiloxane to the metallic body of the active electrode in this manner sufficient for electrosurgery. Still another significant aspect of the invention relates to manufacturing an electrosurgical blade with a nonstick, release coating comprising silicone in a more cost-effective and efficient manner.
In accordance with these and other aspects, the present invention is directed to an electrosurgical blade or active electrode used for conducting electrical energy to tissue during an electrosurgical procedure. The active electrode includes a conductive metallic body having a working area portion and a connection end to which the electrical energy is conducted. The working area portion of the body includes at least one broad side which has been oxidized. A nonstick release coating comprising substantially polysiloxane is directly adhered to the oxidized broad side of the body. The nonstick release coating has a substantially uniform cross-sectional thickness. The oxidation provides sufficient adherence for the nonstick release coating, thereby avoiding the necessity for applying primer coats, multiple coats or roughening the surface to obtain adequate adherence of the release coating. Because it is not necessary to roughen the broad side, there are no peaks and valleys to create point source field gradient effects that might cause unintended arcing through the release coating. The thickness of the coating can be made thinner because there are no peaks which must be insulated to avoid the unintended arcing. The adherence obtained by the oxidized broad surface provides adequate adherence for the release coating, and the extent of oxidation may be controlled to achieve the maximum adherence.
Also in accordance with the above noted aspects, the invention relates to a method of manufacturing a coated electrosurgical blade or active electrode from a conductive metallic body. The metallic body has a working area portion including at least one broad side having smooth and non-roughened characteristics and also has a connection end to which electrical energy is conducted when the active electrode is used in electrosurgery. The steps of the method involve oxidizing an element of the metallic body over the broad side, uniformly coating the oxidized broad side with a liquid nonstick release material containing substantially polysiloxane, and curing the polysiloxane of the material. The thin liquid coating, when cured, provides a relatively thin and uniform coating to achieve the nonstick release characteristics as described above. These improved characteristics are achieved without the complexity and expense of applying multiple coats of release material or primer material and release material, curing the material between coatings, or manipulating the electrode in complex movements to create special non-natural coating contours.
Preferable features of both the active electrode and its method of manufacture involve thermally oxidizing the broad side under circumstances where the metallic body is stainless-steel and iron in the stainless steel is oxidized into iron oxide. The extent of the iron oxide created is preferably that amount to achieve maximum adherence of the coating. The thermal oxidation is preferably achieved by heating the stainless-steel body in an oxygen containing environment. Preferably, the polysiloxane of the nonstick release material is a thermally curing polysiloxane which does not bloom hair-like fingers during or after curing. The uniformity of the coating extends transversely in cross-section with respect to the longitudinal extent of the broad side. In addition, preferable characteristics of the uniform cross-sectional coating cause it to change or increase in thickness longitudinally from a distal tip of the broad side to a location on the broad side which is more proximal from the distal tip.
The coating is preferably formed in a single layer by dipping. Preferably, the broad surface is vertically oriented to extend downward and the dipping occurs by inserting and withdrawing the broad surface vertically from a pool of the liquid nonstick release material, preferably at a controlled rate to create the uniform coating. Excess material is allowed to drip from the downward extending broad side. Thereafter, the broad side is preferably inverted to extend vertically upward. The upward extension of the coated broad side allows liquid material on the broad side to move away from a distal tip toward a location spaced proximally from the distal tip until a thickness of the substantially uniform coating increases approximately linearly along the length of the broad side from the distal tip to the location spaced proximally from the distal tip, before the polysiloxane is cured. A shank portion of the body preferably includes at least one groove formed adjacent to the working area portion to receive and contain excess liquid coating material applied to the body when the blade is inverted and to avoid having the release material coat any other undesired parts of the active electrode. The metallic body is preferably ultrasonically cleaned and passivated before oxidizing, coating and curing it.